Direct resistance heating in the ohmic reactor

The chemical industry faces the task of comprehensively decarbonizing its processes and converting to CO₂-neutral production. A key lever for this is the electrification of chemical processes through innovative technologies such as directly resistance-heated reactors. These reactors use electrical energy from renewable sources to carry out chemical reactions efficiently and flexibly, largely replacing fossil raw materials.

The detailed objectives of the research are to build such reactors and develop resistance-heated catalyst materials. These technologies are to be demonstrated using practical applications, including the synthesis of basic chemicals such as 1,3-butadiene from bioethanol and the low-emission recovery of hydrogen from ammonia. The focus is on optimizing energy efficiency, process stability, and scalability to ensure transferability to industrial applications.

Direct resistance heating of chemical processes offers outstanding savings potential in terms of energy consumption and CO₂ emissions. Ohmic reactors powered by electricity from renewable energies are characterized by virtually loss-free energy transfer, which can save up to 20–30% of energy compared to conventional processes. In addition, the reaction temperature can be controlled, increasing process stability and flexibility. With their high efficiency and the ability to completely replace fossil fuels, ohmic reactors are significantly advancing the electrification and decarbonization of the chemical industry.

The progress achieved covers several key areas:

1. Catalysts and reactor development

The development of electrically conductive catalyst shapes has been successfully advanced. These catalysts have been produced in various forms, such as solid ceramic bodies or highly porous foam structures (e.g., SiC foams), which can be efficiently integrated into the processes. These materials enable direct electrical resistance heating, allowing precise control of temperature and reaction conditions. The adaptation of reactor designs to specific requirements was also addressed in order to optimize process stability and efficiency.

2. Ammonia cracking

Initial tests on the decomposition of ammonia have shown that hydrogen recovery can be efficiently implemented using electrically heated reactors. Compared to conventional approaches, which involve indirect heating with high energy losses, the new systems allow effective heat transfer directly into the catalyst bed.

3. Simulation methods

The further development of mathematical modeling and simulation methods has been successfully implemented. This has enabled the microstructures of the reactors to be virtually mapped in order to precisely simulate complex processes such as mass and heat transport. Based on these models, temperature and energy profiles as well as the kinetic processes of the chemical reactions were predicted. This resulted in a validated basis that enables optimization of process parameters early in development and allows the reactors' geometry to be tailored specifically for higher performance and efficiency. These interim results pave the way for energy-efficient, scalable, and low-greenhouse-gas technologies that have the potential to transform key processes in the chemical industry in a sustainable manner.

• Fraunhofer Institute for Silicate Research ISC
• Fraunhofer Institute for Industrial Mathematics ITWM